Relay with voltage compensation



Mara 18. 1969 J. w. WASELESKI, JR., ET L 3,434,089

RELAY WITH VOLTAGE COMPENSATION Filed Jan. 5, 1966 Sheet of 5 INSl/LAT/ON 'J C :1 cl: :1 q 1| I. (I r I 1 58 6 0 46 I26 .94

I 72 ve 72 tons:

fiance's J? Baiting, Joseph 1V. WaseZeskijJR BernardJMKuZwicki,

March 18, .1969

J. w. WASELESKI, JR., ET AL 3 ,434,089

RELAY WITH VOLTAGE COMPENSATION Sheet ,3 of 3 l Filed Jan.

Fan 0215 Joseph T4 WaseZeskgqR ernardMKuZwz'ch' Z14,

March 18, 1969' J.W. WASELESKI, JR., ET AL 3,434,089

RELAY WITH VOLTAGE COMPENSATION Filed Jan. 5. 1966 7 Sheet 3 of 3TEMPERA TURE "c A- 8.4 1.61 3 "no CERAMIC. 5- CARBON BLACK LOADEDCROSS-LINKED POLYETHYLENE. c asog aaaa aooa 3 CERAMIC by /4., 1% Att y,

United States Patent 6 Claims ABSTRACT OF THE DISCLOSURE A relay inwhich a snap acting switch cooperates with a thermally responsiveactuating means comprsing two bimetallic blade members which provideambient compensation so that a change in ambient temperature will causethe blades to tend to move in opposite directions against each other. Aheater is provided to heat one of the blades to a temperature differentthan the other blade causing movement of both blades and consequentactuation of the snap acting switch through a motion transfer pin. Theheater in one embodiment comprises a plurality of pills constructed ofmaterial having a steep-sloped, positive resistivitytemperature curve(PTC) electrically connected in parallel. Another embodiment shows a PTCheater pill mounted on a support with an air gap of a predetermined sizeseparated the heater from the bimetallic blade to provide a time delayof a desired amount. Still another embodiment shows a cantilever mountedsupport for the heater pill so that the air gap will vary as thebimetallic blade flexes due to heat generated by the heater. The use ofthe PTC material minimizes the effects of voltage variations ontemperature and the use of the air gap as thermal barrier results involtage compensation.

This invention relates to electrical relays and more particularly tothermal time delay relays.

This invention is an improvement over the relay disclosed and claimed inUS. Patent No. 3,205,327, issued Sept. 7, 1965 to Moorhead et al. andassigned to the assignee of the instant invention.

The present invention, while having more general uses, is particularlyuseful in applications for controlling an auxiliary heater for a heatpump (e.g., a space heater) and as a time delay control for airconditioners or for compressors in refrigeration systems.

Among the several objects of this invention may be noted the provisionof an improved thermal time delay relay adapted to control an electricalcircuit; the provision of such an improved thermal relay which includesambient compensated thermally responsive actuating means as well asbeing voltage compensated; the provision of a thermal relay having meansto prevent overheating and burn out problems; the provision of such arelay with rapid response; the provision of a thermal relay of the classdescribed which includes snap-acting switch means; and the provision ofa time delay relay of the class described which is simple inconstruction, compact in form and economical to assemble andmanufacture.

Other objects and features will be in part apparent and in part pointedout hereinafter.

The invention accordingly comprises the elements and combination ofelements, features of construction, and arrangements of parts which willbe exemplified in the structures hereinafter described and the scope ofwhich will be indicated in the appended claims.

In the accompanying drawings in which several of the various possibleembodiments of the invention are illustrated:

FIG. 1 is a top plan view of a switch according to the presentinvention;

FIG. 2 is an enlarged sectional view taken on line 2--2 of FIG. 1;

FIG. 3 is a bottom plan view of the switch shown in FIG. 1; and

FIG. 4 is a partial top plan view of a second embodiment of the presentinvention;

FIG. 5 is a vertical cross section taken on line 5-5 of FIG. 4;

FIG. 6 is a view similar to FIG. 5 but showing a third embodiment of theinvention; and

FIG. 7 shows resistivity v. temperature. curves for several materialsuseful in our invention.

Similar reference characters indicate corresponding parts throughout theseveral views of the drawings.

Dimensions of certain of the parts as shown in the drawings may havebeen modified and/ or exaggerated for the purposes of clarity ofillustration.

Referring now to FIGS. 2 and 3, there is shown a time delay thermalrelay according to the present invention and generally indicated atnumeral 10. Relay or switch 10 includes a housing 12 formed of aconventional electrically insulating material such as a moldablephenolic resinous material. As best seen in FIG. 2, housing 12 includesa base 14 and a peripherally extending skirt portion 16 on one sidethereof, defining a cavity 18 for reception therein of electricallyconductive snap-acting switch means generally indicated at numeral 40.Housing 12 also includes a plurality of upstanding wall portions 20, 22,24 and 26 on the other side of base 14 which define a cavity 30 forreception of thermally responsive actuator means generally indicated at70 and which will be described in greater detail below. Cover members(not shown) may be connected to the housing 12 to close cavities 18 and30 after assembly of switch 10 has been completed.

Snap-acting switch means Referring now to FIG. 3, snap-acting switchmeans 40 is received within housing cavity 18 and comprises anelectrically conductive flexible blade 42 cantilever mounted adjacentone end 44 thereof, on base 14. End 44 is firmly clamped between, andsecured to base 14 and an electrically conductive terminal 46 by meansof a rivet 48 which also electrically connects blade 42 to terminal 46.The free end of blade 42 carries a pair of electrical contacts 50 and 52on opposite sides thereof, as best seen in FIG. 2, for alternateengagement, respectively, with electrical contacts 54 and 56 which arerespectively carried by electrical terminals 58 and 60. Housing 12supports and mounts terminals 58 and 60 on opposite sides of blade 42and in the path of movement thereof, as best seen in FIGS. 2 and 3.Contacts 50, 52, 54 and 56 are formed of a suitable electricalcurrent-conducting material such as silver or the like. Blade 42 isformed of a suitable highly electrically conductive spring material suchas, for example, a beryllium-copper alloy or a Phosphor bronze alloy.

To provide for snap-acting movement of the flexibleblade 42 to actuatethe contacts, a spring member 62 is provided which is flexed into aU-shaped form (as seen in FIG. 2), with one end thereof connected withthe blade 42 adjacent the contact-carrying end thereof, and the otherend of the spring member connected with a centrally located tongue 64formed integrally with the blade 42 as by blanking out portions of thecenter of the blade. Tongue 64 extends from its integral connection withend 44 of the blade toward the free contact-carrying end of the blade.As best seen in FIGS. 2 and 3, tongue 64, ad-

jacent its interconnection with spring 62, is provided with a dirnpledor raised abutment portion 66 for engaging a motion transfer member tobe described in greater detail below.

The tendency of the spring 62 to straighten out urges blade 42 eitherupwardly or downwardly as seen in FIG. 2, depending upon the position oftongue 64. Snap-acting means 40 can be either of the so-called bistableor monostable types, depending upon the spacing between the stationarycontacts 54 and 56 relative to the neutral position of the blade 42,movement beyond which in either direction will cause snap-acting orover-centering movement. Switch means 40, as illustrated by way ofexample in FIG. 2, is of the monostable type and contacts 52 and 56 arenormally closed, so that upon removal of a force applied against tongue64 to cause snap opening of contacts 52 and 56, blade 42 willautomatically snap back to the FIG. 2 solid line position to reclosecontacts 52 and 56.

Thermally responsive actuating means Switch also includes a thermallyresponsive actuating means generally indicated at numeral 70 for causingsnap action of means 40 to effect contact actuation. Means 70 comprisestwo blade members 72 and 74, each of which are formed of a compositebimetallic thermally responsive material having a relatively highexpansion component and a relatively low expansion component, as bestseen in FIG. 2. Member 72, as best seen in FIG. 1 is in the form of aframe and provides a substantially rectangular shaped window opening 76which is defined by four legs 78, 80, 82 and 84. Member 72 can be formedfrom a sheet by a simple punching or blanking operation. Member 74 issubstantially T-shaped and includes a transversely extending end portion86. As best seen in FIGS. 1 and 2, end portion 86 and leg 84,respectively, of bimetal members 74 and 72 are arranged in stackedoverlying relationship and mutually separated by a thermally andelectrically insulating strip 90 formed, for example, of mica. Thisstacked assembly is cantilever mounted on an extension 92 of anelectrically conductive terminal member 94 by means of a pair of rivets96. A thermally and electrically insulating strip 98 (formed, forexample, of mica) separates bimetal member 74 from terminal portion 92.Rivets 96 not only serve to firmly cantilever mount the bimetalblade-insulator assembly but also serve to electrically connect bimetalmember 72 with terminal 94. A lost motion connection for the other endsof bimetal members or blades 72 and 74 is provided by a bifurcatedportion on the other end of member 74 as defined by fingers 102, 104 and106, which receive and sandwich therebetween, leg 80 of member 72. Thisconnection permits relative sliding movement between the free ends ofmembers 72 and 74 in a direction along the plane of these members, toavoid creating undesirable stresses and also confines upward anddownward movement (as seen in FIG. 2) of the free ends of these membersto movement in unison. Leg 80 is provided with a dimpled portion 110which is positioned to engage one end of a motion transfer pin 112 whichis slidably received in an aperture 114 provided by base 14 of thehousing 12. The other end of pin 112 is positioned to engage the dimpledportion 66 on the central tongue 64 of the snap-acting blade 40 to causetongue 64 to move in response to unitary movement of bimetal members 72and 74 to effect snap-acting motion of blade 40.

In practice terminal 94 and bimetal blades 72 and 74 are made up as aseparate subassembly which is thereafter mounted on the housing by meansof a threaded fastener 100. The bimetal members 74 and 72 are arrangedand constructed to provide for ambient compensation. In this regard theinside bimetal components of the blades as are nearest one another orthose which face one another, have relatively similar coefficients ofthermal expansion, i.e., these components either both have relativelylow coefiicients of thermal expansion or both have relatively highcoetficients of thermal expansion. It is preferred (but not essential)that blades 72 and 74 be formed of the same or similar bimetal material.It will be seen from the above that when blades 72 and 74 are subjectedto a change in ambient temperature (e.-g., an increase) that the bladeswill tend to flex or move in opposite directions against each otherwhich opposing movement will effectively cancel each other out tothereby prevent or at least minimize movement of blades 72 and 74 as aunit in response to changes in ambient temperature. Upon heating ofmember 74 to a temperature different from that of member 72, member 74will exert a flexing force against member 72 which is greater than theopposing flexing force exerted by member 72 against member 74, whichwill cause the free ends of members 72 and 74 to move in unison eitherdownwardly or upwardly depending on whether the inside components of theblades have relatively low or relatively high coeflicients of thermalexpansion. In the exemplary embodiment shown in the drawings, the insidecomponents of the blades have relatively low coefiicients of thermalexpansion so that upon suitable differential heating of member 74,downward movement (as seen in FIG. 2) in unison of the free ends ofmembers 72 and 74 will take place.

Relay 10 includes an electrical heater 119 which, in the FIGURES 1-3embodiment, comprises a plurality of pieces or pills 120. Three areshown but the number is a matter of choice. Electrically conductinglayers 122 and 124, formed of silver, for example, are attached in aconventional manner to opposite faces of each pill 120. Pills 120 arelocated in close thermal juxtaposition to bimetal member 74, and in theFIGS. l-3 embodiment is electrically separated therefrom by a layer ofelectrically insulating material 126, which may, for example, be mica.Layers 122 are electrically connected by conductors 125 to anelectrically conductive terminal 126 which is located intermediateupstanding portions 24 and 26 of housing 12 and secured to base 14 bymeans of rivet 127.

Layers 124 are electrically connected by conductors 128 to bimetalmember 72 which is in turn electrically connected to terminal 94.

As seen in FIGURE 1, pills 120 are electrically connected in parallel.Pills 120 are constructed of material which has a steep-positive-slopedresistivity-temperature curve (hereinafter referred to as PTC material).This will be explained in greater detail below.

Heater 119 may be mounted, as seen in FIGURES 4 and 5, by mounting pill120 on layer 132 of an electrical and thermal insulation material suchas a polycarbonate, which is separated from bimetal member 74 byportions or bosses 130, 131 to produce an air gap of a predeterminedsize. The time required for member 74 to flex due to differentialheating is dependent upon the thermal conductivity between the heaterand member 74. Thus it will be seen that by providing a predeterminedthermal insulation barrier between pills 120 and member 74 a giventime-delay can be built into the device. The air gap is, of course, athermal insulator. It will be obvious that other thermal insulationmaterial can be used to effect the same result.

FIGURE 6 shows a similar mounting but utilizes only one mounting portionor boss 131 so that the air gap between heater 119 and bimetal 74 willvary as bimetal 74 flexes due to heat generated by heater 119. Thusgreat flexibility can be effected in the opening and closingcharacteristic of the switch by the mounting of the heater elements asdescribed.

Operation of relay 10 is as follows: Contacts 52 and 56 are normallyclosed, as shown in the FIG. 2 solid line position of the parts. Upon achange in ambient temperature (e.g., an increase) bimetal blades 72 and74 will tend to flex in directions opposite to each other to producesubstantially equal opposing forces with the result that little or nomotion of the bimetal members takes place. However, when heater 119 iselectrically energized (by the circuit in which terminals 94 and 126 areconnected),

member 74 becomes heated to a temperature different from that of member72. This results in a downward flexure force (as seen in FIG. 2) exertedby member 74 which is greater than the opposing upward flexure forceexerted by bimetal member 72 causing downward movement in unison of thefree ends of members 74 and 72 from the solid line to the broken lineposition shown in FIG. 2. This causes motion transfer member 112 to movedownwardly (within opening 114) against the dimpled portion 66 of thetongue 64 to move the latter to the FIG. 2 dashed line position to causeover-centering or snap movement of the blade 42 from the FIG. 2 solidline contacts 52, 56 closed, and contacts 50, 54 open position to theFIG. 2 broken line contacts 52, 56 open and contacts 50, 54 closedposition. Contacts 50 and 54 will remain closed (in the FIG. 2 brokenline position) as long as motion transfer pin 112 is maintained in thebroken line position by the forces exerted against it by the bimetalblades 72 and 74. Upon sufiicient diminishing of the current in theheater 119, or upon deenergization of tht heater, bimetal member 74 willcool and the blades 72 and 74 return to the FIG. 2 solid line position,and blade 42 will automatically snap back to the solid line FIG. 2position to reclose contacts 52 and 56.

The U-shaped portion of frame 72 defined by legs 78, 80 and 82 whichprojects from the cantilever mounted end leg 84 advantageously isrelatively thermally isolated from heater 119 by the spacing betweenlegs 78 and 82 from blade 74 which is positioned therebetween in thewindow opening 76, as best seen in FIG. 1. By this arrangement, blade 72does not become heated to any substantial extent by heater 119.Insulators 90 and 98 further serve to minimize heat transfer betweenblades 72 and 74 and between heater 119 and blade 72 so that the heatgenerated by heater 119 is directed primarily to the blade 74 to raisethe temperature of the latter above that of the ambient compensatingblade 72 to produce desired contact actuating motion of the free ends ofthese members. However, total thermal isolation between bimetal blade 72and 74 is not desired because by allowing some heat to be conducted fromblade 74 to blade 72, faster resetting of contacts 52, 56 can take placewhen the heater current is sufliciently diminished or removed. Locatingmember 74 in the window opening 76 intermediate legs 78 and 82 inaddition to providing for a compact construction also permits asubstantial portion of the length of blade member 74 to liesubstantially in the same plane as or at least very close to the planeof legs 78 and 82, which avoids or at least minimizes creation ofundesirable stresses upon temperature change which might tend to twistor rotate the free end of blade 72. This also simplifies theconstruction and assembly of parts, and provides for compactconstruction. If desired, leg 84 of blade 72 and portion 86 of blade 74can be omitted and the unjoined ends of legs 78, 82 and of blade 74 canbe cantilever mounted in the same plane on terminal 94 so that a greaterportion of member 74 will lie substantially in the same plane with legs78 and 82 to further minimize creation of undesirable twisting stressesand moments at the free ends of these members 72 and 74, when thelatte'r flex in response to temperature change.

In prior art heaters, such as in the patent to Moorhead et al. referredto supra, the time required to raise the temperature of bimetal 74 to atemperature which will actuate the switch (by Joulean heating of theheater) is directly dependent on the applied voltage since heatgeneration is proportional to the voltage squared the applied voltagesince the steady state temperature of the heater also varies as thevoltage squared:

where a. steady state heater temperature T =ambient temperature K=netheat transfer coeflicient Thus a change in voltage will cause a changein the operation of the relay. The actuation time (on time) may, forexample, vary as much as 40% for a voltage change of only 10%. The olftime will also vary but to a lesser degree. Further, too high voltagecan cause overheating and burning of the heater. This is due to the factthat the electrical resistance of such prior art heaters is generallyindependent of temperature.

In accordance with our invention, a heater is used which electricalresistance increases rapidly in region of the control temperature. Suchmaterial include the semiconducting barium titanate ceramics and certainplastics such as carbon-black loaded, cross-linked polyethylene. FIGURE7 shows typical resistivity temperature curves. Curve A is for Ba- 997La003TiO3; curve B is for carbon black filled, cross-linked polyethylene;and C is for soa nss ooa s- Heaters constructed from such PTC materialscannot overheat due to the tremendous increase in resistance over a verynarrow temperature range. Such heaters selfheat to the controltemperature (located in the near vertical portion of the curves in FIG.7). A change in voltage causes very little shifting of the curves inFIG. 7 so that the temperature is more or less independent of theapplied voltage.

It will be noted that, especially in the FIGURES 4-6 embodiment, if athermal resistance is interposed between the heater and the bimetal suchthat the time required to switch the relay on is long compared to theinduction time of the heater, voltage compensation is achieved.

It will be seen from the above that the present invention provides for athermal time delay relay (the time delay resulting from the timeinterval required for transferring heat from heater 120 to blade 74 andraising its temperature sufiiciently to overcome the opposing fiex-ureforce of blade 72), which is essentially independent of voltage, has arapid response time due to the initial low resistance of the PTC elementyet has a very high resistance at elevated temperature preventingburning out with higher voltage.

In view of the above, it will be seen that the several objects of theinvention are achieved, and other advantageous results attained.

As many changes could be made in the above constructions withoutdeparting from the scope of the invention, it is intended that allmatter contained in the above description or shown in the accompanyingdrawings, shall be interpreted as illustrative and not in a limitingsense, and it is also intended that the appended claims shall cover allsuch equivalent variations as come within the true spirit and scopeofthe invention.

We claim:

1. A voltage compensated electrical switch comprising a base; contactsmounted on the base; thermostatic means including an elongatedthermostatic element mounted on the base to provide contact actuationmotion for the contacts; an elongated generally fiat support having twoends composed of electrical insulating material; a plurality of bossesof thermal insulation mounting the support to and spacing the supportfrom the thermostatic element; and a heater composed of a steep-slopedPTC material located on the support and separated from the thermostaticelement by the support and the spacing whereby the transfer of heat fromthe heater to the thermostatic element is impeded.

2. A switch according to claim 1 in which the PTC material is selectedfrom the group consisting of carbon black filled, cross-linkedpolyethylene and doped barium titanate.

3. A switch according to claim 2 in which the doped barium titanate isBa La TiO 4. A switch according to claim 2 in which the doped bariumtitanate 1S Ba Pb La TiO -5. A voltage compensated electrical switchcomprising a base; contacts mounted on the base; thermostatic meansincluding an elongated thermostatic element mounted on the base toprovide contact actuation motion for the contacts; an elongatedgenerally flat support having two ends composed of thermal andelectrical insulating material; a mounting boss located on one end ofthe support and cantilever connecting the support to the thermostaticelement; and a heater located on the support intermediate the boss andthe other end and spaced from said bimetal, the heater comprising asteep-sloped PTC element selected fi'om the group consisting of carbonblack filled, polyethylene and doped barium titanate, whereby the spacebetween the PTC heater and the thermostatic element will vary withflexing of the thenmostatic element.

6. A switch according to claim 5 in which the PTC element is constructedof a plurality of PTC pills, two electrically conductive layers attachedto spaced portions of the pills, and the pills electrically connected inparallel.

References Cited UNITED STATES PATENTS BERNARD A. GILHEANY, PrimaryExaminer.

R. COHRS, Assistant Examiner.

